Spacer for pancake coils



Feb. 6, 1968 HG JHSWIEFQ 3,368,174

SPACER FOR PANCAKE COILS I Originl Filed May 21; 1962 I 3 Sheets-Sheet 1F ig. IA

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' SPACER'FOR P-ANCAKE (SOILS Original Filed May 21, 1962 a Sheets-ShetgFi g.2B

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1? TL B INVENTOR Heinz G. Fischer ATTORNEY H. G. FISCHER SPACER FORPANCAKE COILS Feb, 6, 1968 5 Sheets-Sheet 3 Original Filed May 21 1962.Fig. 68

United States Patent 3,368,174 SPACER FOR PANCAKE COILS Heinz G.Fischer, Muncie, Ind., assignor to Westinghouse Electric Corporation,Pittsburgh, Pa., a corporation of Pennsylvania Original application May21, 1962, Ser. No. 196,089, now Patent No. 3,252,117, dated May 17,1966. Divided and this application Oct. 11, 1965, Ser. No. 494,506

3 Claims. (Cl. 336-60) ABSTRACT OF THE DISCLOSURE An insulating andspacer member for axially separating pancake type coils in an electricaltransformer. The insulating and spacer member is formed of a sheet ofelectrical insulating material having spaced ridges and furrows, whichform first and second wavy opposed surfaces, the extremities of whichlie on spaced parallel planes and define the axial dimension of themember. The insulating and spacer member has a plurality of transverseopenings therein which extend completely through the member, and whichco-operate with the ridges and furrows to direct cooling fluid in thetransformer both longitudinally and transversely to said member.

This is a division of application Serial No. 196,089, filed May 21,1962, now US. Patent 3,252,117, issued May 17, 1966.

This invention relates to windings for electrical inductive apparatus,such as transformers, and more particularly to an arrangement ofinsulation and conductors in the windings of such apparatus.

A method commonly used to construct windings for inductive apparatus isto form a flat disc or pancake type coil from a main conductorcomprising a plurality of strands or conducting elements. When thecurrent requirement of the apparatus is high, a sufficient number ofthese thin pancake coils are connected in a parallel circuitrelationship to provide the necessary quantity of conducting material,or the number of strands per conductor has to be increased and the coilsare connected in a series circuit relationship. In both cases amultiplicity of brazed joints are necessary to connect the individualcoils. The plurality of parallel or series connected coils are separatedby thin spacers or Washers which give support to the coils and stillprovide channels or paths which allow a cooling medium to flow inthermal communication with the coils.

When the current requirement of an inductive electrical apparatus ishigh, it would result in lower manufacturing costs if the winding couldbe constructed of coils having a larger quantity of conducting material,making it unnecessary to have a multiplicity of brazed joints. However,other problems must be solved if a coil having a large quantity ofconducting material is to be as eflicient as a plurality of conventionalcoils connected in a parallel or series circuit relationship.

One such problem is the fact that eddy current losses in a copperconductor of an inductive apparatus, such as a transformer winding, varywith the square of the dimension of the conductor at right angles to thedirection of the leakage flux, which in the case of the interleaved typeof winding, is approximately at right angles to the axis of the windingor in the plane of the winding coils. To improve efiiciency of theelectrical inductive apparatus, these eddy current losses are reduced inmagnitude by subdividing the required conductor area into a plurality ofparallel connected conducting elements or strands, which thereby reducesthe dimension of the conductor at right angles with the direction of theleakage flux. The conducting strands or subdivided conductor elementsare insulated from each other with paper, enamel, or other ice suitableinsulation, and the several strands are wrapped or taped together toform a single conductor structure from which a coil is wound. Althoughthe method just described reduces the eddy current losses in thewindings of a transformer, there is an offsetting increase in losses dueto circulating currents between the parallel connected strands orsubdivided conducting elements. Losses due to circulating current in awinding whose coils are formed from parallel connected strands can bereduced by transposing the relative position of the strands with respectto the direction of the leakage flux. This transposing of the strandsprevents some strands from being longer than others When they are woundconcentrically, and averages out the fact that the self inductancecaused by leakage flux is different in the individual strands.

Where the number of strands is small, as in the commonly used pancaketype coil, the transposition of the strands can be easily accomplished.However, where high currents must be carried by the winding, severalstrands must be used and the transposition ofthe strands presents agreater problem. Cables with a multiplicity of transposed strands whichare currently available have many disadvantages in that the conductingstructure or cable dimensions increase at the transposition points andthe strands spring apart and rub the edges of adjacent strands when theconducting structure or cable is bent with a small radius. It is,therefore, desirable to provide a winding for electrical inductiveapparatus having a high current capacity and a plurality of conductingstrands. The winding should have a new and improved transposition methodto reduce losses due to eddy currents and circulating currents, and atthe same time present a high degree of safety from short circuitsbetween adjacent strands in the conducting structure or cable.

Further, since the coil having a large quantity of conducting materialis thicker than the conventional pancake coils, cooling the coilsbecomes a major problem. The method commonly used to insulate adjacentpancake type coils involves cutting diamond or rectangular blocks from afibrous material and gluing them in a definite predetermined pattern ona thin board formed of a fibrous material. This insulating board orwasher insulates and supports adjacent coils and still allows a path forflow of the cooling medium between the coils. This process ofconstructing the insulating washer, however, is slow and expensive. Itis, therefore, desirable to provide a winding for electrical inductiveapparatus having a high current capacity and a plurality of conductingstrands that has a new and improved cooling method and a new andimproved insulating washer to separate the adjacent .coils in thewinding.

Accordingly, it is an object of the invention to provide a winding forelectrical apparatus having an improved insulation arrangement and moreefficient path for the flow of the cooling medium.

Briefly, the present invention accomplishes the above cited object byproviding a Winding for electrical apparatus which is suitable for highcurrents without brazing a multiplicity of coil sections in parallel orseries.

The coil is comprised of a large number of conducting strands perconducting structure and is provided with an improved method fortransposing the conducting strands. It is also provided with a new andimproved method for cooling the coil turns and a new insulating washerfor insulating adjacent coils and provide an improved path for flow of acooling medium.

Further objects and advantages of the invention will become apparent asthe following description proceeds and features of novelty whichcharacterize the invention will be pointed out in particularity in theclaims annexed to and forming a part of this specification.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings, in which:

FIG. 1A is a plan view of a coil of the type in which this invention maybe employed;

FIG. 1B is a cross-sectional view, taken on line lB-IB of FIG. 1A,showing the relative locations of the conductors and insulating members,and the cooling method employed in this invention;

FIGS. 2A and 2B are cross-sectional views showing construction of mainconductors that may be used to form the coil of FIGS. 1A and 113;

FIG. 3A is a plan view of a coil showing a coil turn formed of aplurality of conductors;

FIG. 3B shows the cross point between two coils;

FIGS. 4A and 4B show how the starting length of a coil is brought outand how the strands are bent to form the starting length;

FIGS. SAand 5B are right and left-hand isometric views showing thetransposition method used in the coil of FIGS. lA'and 1B;

FIG. 5C shows the transposition sequence of the subdivided conductorswithin the coil of FIG. 1;

FIGS. 6A, 6B and 6C show the side elevation, top plan view and endelevation respectively of an insulating member which is used to insulateadjacent coils;

FIGS. 7A, 7B and 7C show another embodiment of the invention; and,

FIG. 8 shows how the insulating member used to in sulate adjacent coilsmay be cut from one sheet of in sulating material.

Referring to FIG. 1A of the drawings, a coil 10 of the type shown may beformed from a main conductor 12 comprising a plurality of parallelconnected strands or subdivided elements 14. FIG. 2A shows a crosssection of the main conductor 12 shown in FIG. 1A, illustrating ingreater detail the plurality of parallel connected strands 14 and thestrand insulating material 15. If desired, a subdivided strand 11, asshown in FIG. 2B may be used instead of the single wire strand 14. Thesubdivided strand 11 may be used to increase the current capabilities ofthe coil 10 shown in FIG. 1A without increasing eddy current losses orinterfering with the winding procedure. The subdivided strand 11 ishandled in the same manner as the single wire strand 14. The strands 14are insulated from each other by enamel, paper, or other suitableinsulation material 15 and the strands 14 are then taped or wrappedtogether, usually in two layers, to form a solid conducting structure ormain conductor 12. Referring again to FIG. 1A, the main conductor 12 isthen wound into a coil 10, with each turn 16 of the coil 10 insulatedfrom the adjacent turn 16 by an insulating member 18. When very largecurrents are to be carried by the coil 10, or for other considerations,it may be desirable to connect a plurality of conductors 12 in parallel.FIG. 3A illustrates a coil 80 with two conductors 82 and 84 connected ina parallel circuit arrangement. The conductors 82 and 84 are crossed atthe start 86 and finish 88 connections if more than one coil 80 perwinding is used. An insulating material, such as pressboard is used tofill the space 90. FIG. 3B shows the crossing point between two coilsviewed from point 3B in FIG. 3A. Connecting a plurality of conductors inparallel also improves the balance in a transformer as it allows aplurality of coils 80 to be connected in a series circuit relationinstead of the parallel circuit relation that would be used for coilsusing a single conductor. An insulating member 18 may be used betweenthe parallel connected conductors 82 and 84. Referring again to FIG. 1A,the insulating member 18 not only serves to insulate adjacent turns 16,but it spaces the turns and provides a path for a cooling medium only.This transverse or cross-flow of cooling medium through the coil makespossible the use of a coil having a multiplicity of conducting elements,because each conducting element in the main conductor is cfficiently andadequately cooled.

The insulating member 18 used to insulate adjacent turns must not onlyhave good insulating qualities, but it must also have the strength tosupport the turns and still provide an adequate path for flow of acooling medium. A fibrous material, shaped into continuous -'cor-'rugations, has been found to provide these necessary qualities and isvery easy and economical to manufacture. FIG. 1A also shows quartersections of a new insulation member 30 and 31) used to support andinsulate adjacent coils. This insulating spacer washer 30 and 30' willbe described in detail hereinafter.

Where one, or an odd number of these cross flow type coils are used perwinding group, the start conductor-is brought out, as illustrated byconductor 12 in FIG. 1A. The standard type coil in use today commonlyuses a prepared conductor, consisting of a plurality of insulated andtransposed strands, brazed to the coil start 17. The transpositions arenecessary in this prepared conductor because when the prepared conductorcrosses the coil 10 adjacent to the turns 16, the prepared conductor issubjected to a very strong stray field, and because of the relativelyshort distance between the brazed joint of the prepared conductor to thecoil start and the brazed joint to a bushing cable or similarconnection.

The design characteristics of the cross flow type coil, however, makethe use of a separate prepared conductor and the accompanying brazedjoint unnecessary. The cross flow type coil has a very long strandlength per coil and the resistance of the strand loop is, therefore,relatively high. This higher resistance makes it practical to use thestrands from the conductor that forms the coil to take the place of theprepared conductor, and transposition of the strands is unnecessaryduring this starting length. FIG. 4A shows in detail how the strands 14are brought out to form the starting length of the conductor 12 for thecoil 10. The strands 14 are bent so the two layers of strands 14 thatform conductor 12, form one layer of wires while crossing the turns 16of the coil 10. FIG. 4B shows the bending of the strands 14 of theconductor 12 to form one layer, viewed from point 4B-4B in FIG. 4A.

FIG. 1B is a cross-section, taken on line 113-113 of FIG. 1A, with therelative location of adjacent coils 31, insulating spacer washers 30,and flat pressboard washers 29 shown to illustrate the cooling mediumflow path in detail. The coolant enters the coil at arrow 26 and leavesat arrow 28. To insure that the coolant traverses the coil throughpassageways 19 formed by the insulating members 18, the upper end oflongitudinal passage 20 is blocked with a suitable member 22. The otherlongitudinal passageway 21 is blocked at the lower end with a member 24.With this arrangement of passageways, the cooling medium is forced toflow into the coil longitudinally at arrow 26 and along passage 20formed by insulating spacer washer 30. Adjacent coils 31 are separatedby a flat washer 29 formed of a pressboard or other suitable material.Since passage 20 is blocked by member 22, the coolant can only flowthrough the openings 19 between the turns 16 provided by the insulatingspacers 18. When the coolant reaches passage 21, it cannot flow downwardbecause of blocking member 24. Therefore, the coolant must flow throughinsulating spacer washer 30- and from the coil at arrow 28. It canreadily be seen from FIG. 1B

- that this cross-flow cooling arrangement causes the coolto flow acrossthe coil and in thermal communication 1 with each coil turntransversely. The thin pancake coils in common use provide for coolantto flow longitudinally ing medium to come into thermal communicationwith every conducting strand, and, therefore, making possible the use ofa large number of conducting strands and hence the design of a very highcurrent coil. To accomplish this cross-fiow cooling design, aninsulating spacer or washer 30 and 30' was developed to insulate andspace adjacent coils and at the same time provide the passageways and21, shown in FIG. 1B. It is not only desirable that this insulatingwasher adequately insulate adjacent coils but it must provide theshortest free copper length, or distance between adjacent supports, togive support to the coil turns under normal and short circuitconditions. However, the obtaining of the shortest possible free copperlength should not be accomplished at the expense of covering a largepercentage of the coil surface with the insulating washer, as this wouldunduly hinder the flow of cooling medium.

A method commonly used to form these insulating washers consists ofcutting specially shaped blocks from a fibrous material and gluing themto a fiber board in a predetermined pattern. This process is laboriousand results in a spacer washer that produces a free copper length of twoand three-quarter inches and covers approximately twenty percent of thecoil surface.

FIGS. 6A, 6B and 60 show a new spacer washer developed for use in thecross-flow coil. This new spacer washer 30 completely eliminates thecutting and gluing of blocks. The washer consists of a heavy insulatingboard 30, corrugated or folded and shaped into parallel ridges andfurrows so as to form a wavy surface. Points 32 on the spacer washer 30contact and support adjacent coils and the cooling medium flows in thechannels 34. To allow the cooling medium to flow transversely to theinsulating spacer, as well as longitudinally, and hence allow all thecooling medium to traverse the coil, the washer 30 must have a suitablenumber of openings 36, as shown in FIGS. 6A and 6B. The openings 36 inthe spacer washer 30 may be milled, punched, sawed or performed in someother suitable manner. If the openings 36 in the v spacer 30 are formedby a saw cut, the openings 36 will be in line across the washer 30, asshown in FIGS. 6A and 613. If the openings 36 are formed by punching, orby some other suitable method, the openings 36 may be placed in anydesirable pattern, as shown in FIGS. 7A, 7B and 7C.

The spacer washer 30 not only provides an insulator between adjacentcoils that is inexpensive and easy to manufacture, but it presentsgreater support to the coil turns with less hindrance to the flow ofcoolant than the conventional spacer washer. Using the new design spacerwasher 30, the free copper length is reduced as opposed to theconventional washer. Also, the coil surface has less area covered whenusing the corrugated spacer washer 30than when using the conventionalwasher.

FIG. 8 shows an additional advantage of the new corrugated washer 30 asquarter sections 30 and 30" of the washer 30 may be cut from one largesheet of material 41. FIG. 8 shows how the cut should be made if aradius 42 is desired on the washer. The strips are the only excessmaterial. FIG. 1A shows the quarter sections 30 and 30' and how they areplaced relative to the coil 10.

FIG. 1B shows the individual conducting strands 14, which, as pointedout previously are necessary to reduce eddy current losses. The largenumber of strands 14 and the efiicient cross-flow method of cooling theconducting strands allows the construction of a single high current coil10. However, to reduce circulating currents caused by the large numberof parallel connected conducting strands 14, the strands 14 must betransposed, or continuously shifted about the main conductor 12 or cableaxis without twisting the strands 14, and so that each strand 14successively occupies the same position as is occupied by all the otherstrands 14.

One type of transposition, commonly used with a multiplicity of strands,is called the complete transposition. It involves two layers ofconductors, with all conductors moving at a common transposition pointto the opposite layer and in the mirror image of its original location.In other words, the strand in the upper left corner of one layer ofstrands would move to the lower right corner of the adjacent layer ofstrands and the strand in the upper right corner would move to the lowerleft corner.

This process is followed for all the strands. The completetransposition, however, causes a bulging of the main conductor at thetransposition point and causes ed-ge-to-edge contact of the strands,making necessary the placement of additional insulation of these points.Also, it is diflicult to bend the main conductor in a small radius andimpractical to perform the transposition automatically by a bendingmachine, as the bending angles differ for each strand, depending uponthe number of strands used.

Another transposition, commonly called the full transposition, involvestwo layers of conducting strands, with several transposition pointsrequired to complete one full transposition. With this method, eachstrand moves to the space occupied previously by the adjacent strands.This process is repeated at successive intervals until each strand hasoccupied the same position as is occupied by all the other strands.Cable presently available using the full transposition has disadvantagesin that there is a bulging of the cable at each transposition point andthere is an edge-to-edge contact between some of the strands.Edge-to-edge contact of the strands should be avoided if a high degreeof safety from short circuits is desirable. When the cable is bent intoa coil, the pressure is increased at these edge-to-edge contacts andwhen the coils are pressed during assembly or stressed due to shortcircuits while in operation it is highly probably that the protectiveinsulation will eventually become ineffective. This cable is alsodifiicult to bend flat in a small radius because of a tendency of thestrands to spring apart and distort the cable.

The transposition method developed for use in the cross-flow coilpreviously described eliminates the disadvantages of the methods justdiscussed. FIGS. 5A and 5B show right and left-hand isometric views of amain conductor 50 with'the strands transposed according to theprinciples of the new method. FIG. 5C shows the sequence that may befollowed to accomplish the transposition. In particular, a horizontalbend is made changing conducting strand 1 from one layer or row ofstrands to the other layer or row. Strand 1 is moved into a blank space63 available in the adjacent layer because an odd number of strands isused to form the main conducting structure. This movement of conductor 1can be seen in cross-sectional views 62 and 64 of FIG. 5C. Then, theconductive strands 2, 3,4 and 5, remaining in the layer vacated bystrand 1, are simultaneously bent one conductor space in a verticaldirection. Strand 2 takes the place formerly occupied by strand 1,strand 3 occupies the place previously occupied by strand 2, strand 4occupies the place previously occupied by strand 3, and strand 5occupies the place previously occupied by strand 4. This process leavesa blank space 65 as shown in crosssection 64 of FIG. 5C. At the nexttransition point, the blank space 65 is filled by strand 6, which isbent horizontally, and the strands 1, 9, 8 and 7 remaining inthe layerformerly occupied by strand 6 are bent in a vertical direction, leavinga blank space 67 as shown in crosssection 66 of FIG. 5C. This process isrepeated until one full transposition has been completed, as shown incrosssection 74. As many full transpositions of this type may be usedper cross-flow coil as may be found desirable.

Although, the above description outlines a transposition where theindividual strands move about the main conductor axis in a clockwisedirection, as shown in FIG. 50, it is not meant to be so limited. Forinstance, the first step in the transposition could be a vertical bendby conductors 9, 8, 7 and 6, as shown in crosssection 62 of FIG. 5C,thus filling the vacancy 63. The next step would then be a horizontalbend by conductor 5 into the next layer and the space previouslyoccupied by strand 6. With this method, the strands would rotatecounterclockwise about the main conductor axis.

To maintain dimensions 51 and 53 uniform throughout the length of themain conductor or cable 50, an odd number of conducting strands 52 areused, with the blank space between transposition points occupied withafiller .piece 54 or strip, such as pressboard. Using a filler 54, thecable 50 can maintain auniform shape throughout its length, whether ornot there is a transposition, ;and the dimensions of the cable will notchange. In summary, an odd number of conductors are used so that thefirst bend always moves a strand into the vacant space, leaving a vacantspace for other conductors, and therefore, allowing all the bends to bemade without creating a bulge in the conducting structure.

From FIG. C, it can be seen that at each transposition point, only oneconducting-strand 52 changes from one layer to another, with the otherbends being made within one of the layers. As pointed out previously,this conducting strand always moves into a vacant space which is presentbecause of the odd number of conducting strands. Then the remainingconducting strands, in the layer just vacated by the strands moving tothe other layer, all simultaneously move one space, thus filling thenewly vacated space and creating a space at the other end of the layer.This process is successively repeated until each conducting strand hasoccupied the space occupied by every other strand, and has made acomplete circuit around the axis of the main conductor or cable.

It is. veryimportant that all bends 62 performed in the same layer andall bends 60 moving a strand from one layer to the next be made over avery short distance and not gradually. The distance 58, between thepoint 62 where all strands are simultaneously bent in one layer, to thepoint 62 where all strands are simultaneously bent in the other layer,depends upon the number of transpositions required in one coil. However,this distance should not be too small. For example, in one coil designit was found that a minimum distance 58 of three inches was required.The distance between the bend where one strand 52 changes layers or thehorizontal bend 60, and the bend where all conductors in one layer arebent or the vertical bend 62, is very critical, and should allow enoughspace for the strand which changes layers to move back and forth. Forone coil design this distance was found to be a minimum of three-quarterinch. During distance 56, all strands 52 have flat surface to fiatsurface contact and the horizontal transposition or bend 60 can slideback and forth when the main conductor 50 is bent flat, even over aradius as small as 2 inches, without an edge-to-edge contact andresultant insulation scraping.

\ With this transposition method, all horizontal bends 60 are identicaland all vertical bends 62 are identical. Therefore, the angle of thebends is dependent only on the size of the conducting strand 52 and noton the number of conducting strands used. This makes it practical toaccomplish the bends in a transposing machine. Also, by accuratelybending each strand over a short distance with the sameangle, thestrands have no tendency to spring out of the main conductor or cable 50and there is no bulging or change in cable dimension, even when bentflat over a small radius.

It will, therefore, be apparent that there has been disclosed a new andimproved winding for electrical apparatus. It is a winding that iscapable of carrying high current and yet is efficiently cooled and withlow losses due to eddy currents and circulating currents. Also, it is awinding that has an improved insulating arrangement and more efiicientpath for the flow of cooling medium.

While there have been shown and described what are at present consideredto be the preferred embodiments of the invention, modifications thereof.will-readily occur,

to those skilled in the art. For example, the coil. described applicableto the high voltage side of inductive apparatus. Further, the dimensionsgiven arefor illustrative purposes only and are not to limit in any waythe subjectm'att'er of this invention.

Since numerous changes may be made in 'the abovje described apparatusand different embodiments" or the" invention may be made withoutdeparting from the spirit thereof, it is intended that all the mattercontained -in' the foregoing description or shown in'the accompanyingdrawings shall be interpreted as illustrative, and not in a limitingsense. 1 I claim as my invention: v

1. An insulating and spacer member for axiallysep arating, contacting,and mechanically restraining adjacent pancake type coils in anelectrical transformer containing a cooling medium, comprising: asubstantially flat washershaped insulating structure having apredetermined outer configuration and a central opening therein; saidwasher shaped insulating structure being formed of at least one sheet ofelectrical insulating material, said at least one sheet of electricalinsulating mtaerial having a plurality of spaced ridges and furrowswhich form first and second wavy opposed surfaces, the extremities ofwhich lie on first and second spaced parallel planes and define theeffective axial dimension of the insulating structure; said sheet memberhaving a plurality of transverse openings therein which extendcompletely through said sheet member, and which are defined, at least inpart, by certain of the extremities of its wavy surfaces; said ridgesand furrows and said plurality of transverse openings in said sheetmember cooperating to direct a cooling fluid both longitudinally andtransversely to said sheet mem-, her, when it is disposed betweenaxially adjacent coils of the electrical transformer. 2. The insulatingand spacer member of claim 1 where; in said substantially fiat washershaped insulating structure includes a plurality of said sheet membersdisposed in substantially the same plane and arranged incontactingrelation, to each define a portion of the predetermined outerconfiguration, and a portion of the central open: ing of said washershaped insulating structure. 7 i

3, The insulating and spacer member of claim2wherein the relativedirection of the ridges and furrows is differ: ent in at least certainof said plurality of sheet members.

References Cited LEWIS'H. MEYERS, Primary Examiner. E. GOLDBERG,Assistarzt Examiner.

